IndexMap: Define virtual destructor in .cpp file

This fixes compiler warnings from clang:

src/ccutil/indexmapbidi.h:102:7: warning:
 'IndexMapBiDi' has no out-of-line virtual method definitions;
 its vtable will be emitted in every translation unit [-Wweak-vtables]

Signed-off-by: Stefan Weil <sw@weilnetz.de>

src/ccutil/indexmapbidi.cpp

@@ -21,6 +21,11 @@
 
 namespace tesseract {
 
+// Destructor.
+// It is defined here, so the compiler can create a single vtable
+// instead of weak vtables in every compilation unit.
+IndexMap::~IndexMap() = default;
+
 // SparseToCompact takes a sparse index to an index in the compact space.
 // Uses a binary search to find the result. For faster speed use
 // IndexMapBiDi, but that takes more memory.

src/ccutil/indexmapbidi.h

@@ -41,7 +41,7 @@ class IndexMapBiDi;
 // It must be initialized by copying from an IndexMapBiDi or by DeSerialize.
 class IndexMap {
  public:
-  virtual ~IndexMap() = default;
+  virtual ~IndexMap();
 
   // SparseToCompact takes a sparse index to an index in the compact space.
   // Uses a binary search to find the result. For faster speed use